1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method and a semiconductor device manufactured by the same method, and particularly relates to a method for manufacturing a semiconductor device having a high dielectric gate insulating film made of metal oxide and a semiconductor device manufactured by the same method.
2. Background Art
An MIS (Metal Insulator Semiconductor)-type transistor, which is operated by use of either electrons or holes as carriers, is known as one type of semiconductor devices.
With reference to FIG. 9, in a MIS-type transistor, a gate electrode 55 is formed through a gate insulating layer 54 on both an N-type source region 52 and a drain region 53 formed on a P-type semiconductor substrate 51, and a source electrode 56 and a drain electrode 57 are formed respectively on the source region 52 and drain region 53. This type of transistor is operated by the operating principle that a drain current Id flowing through both regions 52 and 53 is controlled by controlling the concentration of a carrier induced in a channel directly beneath the gate insulating film 54 by a control voltage (gate voltage) VG applied to the gate electrode 55.
Here, the MOS (Metal Oxide Silicon) type transistor using silicon as a semiconductor substrate and silicon oxide as a gate insulating film 54 is widely adopted as a constituent element for LSI (Large Scale Integrated) circuits because of its simple structure and ease of producing large-scale integrated circuits.
In semiconductor devices having the above-described gate insulating film or the gate oxide film, a fundamental condition for improvement in the performance of the semiconductor devices with respect to operating speed and operating capacity is an increase in the drain current. The drain current Id is shown by the following equation.
Idxe2x88x9dACoxxe2x80x83xe2x80x83(1)
where, A represents a proportional constant, and Cox represents the capacitance of the gate insulating film.
The capacitance of the gate oxide film Cox is expressed by the following equation (2).
Coxxe2x88x9dxcex5ox/toxxe2x80x83xe2x80x83(2)
where, xcex5 ox represents the dielectric constant of the gate oxide film and tox represents the thickness of the gate oxide film.
As is clearly shown in Equation (1), the drain current Id can be increased by increasing the capacitance Cox of the gate insulating film and the capacitance Cox can be increased by forming a thin gate oxide film, as shown in the equation (2).
Thus, conventionally, in a semiconductor device having the gate oxide film, the oxide film is formed thinner with the aim of improving the performance of the semiconductor device.
However, when the thickness tox of the gate oxide film is too thin, a gate leak current flows through this very thin gate oxide film; therefore the thickness of the gate oxide film is limited so that the gate leak current can be prevented. In general, it is known that, when the thickness of the gate insulating film is less than 3 nm, the gate leak current begins to flow, and when the thickness of the gate insulating film becomes less than 1.5 nm, a limit is reached for normal operating performance of the semiconductor device.
As shown by Eqaution (2), it is anticipated that the performance of this type of semiconductor device can be improved by forming an insulating film with a higher dielectric constant than that of the oxide film (dielectric constant is 3.8 to 4.1), in addition to forming the thin gate oxide film. Metal oxides such as zirconium oxide (the dielectric constant xcex5 is 10 to 20) are known to have higher dielectric constants, and thus it is possible to produce insulating films with a higher dielectric constant by use of metal oxides having a dielectric constant higher than that of silicon oxide.
The performance of the semiconductor device can be improved by forming the gate insulating film by use of a material having a high dielectric constant while depositing the film within a thickness range, which allows the prevention or reduction of the generation of a gate leak current.
Two representative methods are conventionally known for forming an insulating film having a high dielectric constant for manufacturing a semiconductor device using an insulating film having a high dielectric constant. One method is a sputtering method. FIG. 11 illustrates a schematic representation of the high dielectric constant insulating film by a sputtering method. The sputtering method is explained for the case of forming a ZrO2 film. In a reaction chamber 61, a silicon substrate 62, which is to be deposited, is placed on a susceptor 63 and a Zr target is arranged above the susceptor 63 facing the silicon substrate 62.
In the above arrangement, when plasma 65 is generated in the reaction chamber 61 retained in an atmosphere including oxygen (oxidizing gas) at a desired pressure, plasma ions advance toward the direction of an arrow 66 and impinge the Zr target 64. The impinging ions recoil zirconium ions from the target toward the direction of an arrow 67, the zirconium ions react with surrounding oxygen to form zirconium oxide (ZrO2), and the zirconium oxide is deposited on the silicon substrate 62 forming a film.
Another method for forming the zirconium oxide film is to apply a CVD method. FIG. 12 illustrates a schematic representation of forming a high dielectric constant insulating film by the CVD method. A method for forming a ZrO2 film is described below as an example of forming the high dielectric constant insulating film. In a reaction chamber 71, a silicon substrate 72 for depositing the film is placed on a susceptor 73 and a showerhead 74 is arranged above the susceptor 73 facing the silicon substrate 72. The CVD system is constituted such that a metal organic (MO) material 75 containing zirconium such as Zr(DPM)4, and a flow-meter (mass flow meter) are provided at the outside of the reaction chamber 71, and the thus formed vaporized organic metallic materials and oxygen (oxidizing gas) as the oxidizing agent 78 are introduced into the reaction chamber 71 with an Ar carrier gas 77 through a gas introduction passage 79 from the showerhead.
Using the above-described constitution, the vaporized organic metal material 75 and oxygen gas 78 is carried by the Ar carrier gas 77 and introduced into the reaction chamber 71, while the reaction chamber is maintained at a desired temperature and a desired pressure. In the reaction chamber, the organic metal material 75 is decomposed into metal zirconium and zirconium oxide is formed by the reaction between the metal zirconium and oxygen and deposited on the silicon substrate. A semiconductor device is manufactured using of this zirconium oxide film as the gate insulating film having a high dielectric constant.
However, a problem arises in the above-described semiconductor devices formed by conventional manufacturing methods, such as the sputtering method or the CVD method, in that the performance of these semiconductor devices are degraded. The degradation of the performances of the semiconductor devices is caused by the oxidizing gas used in the conventional manufacturing methods, since the oxidizing gas forms a silicon oxide film having a low dielectric constant in between the gate insulating film having a high dielectric constant and the silicon substrate.
That is, when the oxidizing gas is used for forming the high dielectric constant insulating film by the sputtering method or the CVD method, the oxygen gas used as the oxidizing gas oxidizes the surface of the silicon substrate. As a result, as shown in FIG. 10, in the semiconductor device manufactured by the above method, a silicon oxide film is formed between the high dielectric constant gate insulating film 70 and the silicon substrate 51.
As shown in the semiconductor device in FIG. 10, since the gate insulating film 70 having a high dielectric constant (for example, ZrO2 film: the dielectric constant is 10 to 25) is formed on the silicon oxide film 60 (dielectric constant is 3.8 to 4.1) on the silicon substrate 51, the gate insulating film is substantially composed of these two insulating films 70 and 60. Accordingly, as is clear from the above Equation (2), the capacitance of the gate insulating film in this case decreases, and an increase in the drain current Id is hindered so that high performance of the semiconductor device is not obtainable.
The present invention was made in order to solve the above-described problems. The object of the present invention is therefore to provide a method for manufacturing a semiconductor device having a high dielectric constant gate insulating film made of a metal oxide formed on a silicon substrate.
According to the first aspect, the manufacturing method comprises the steps of placing the silicon substrate into a reaction chamber, introducing an organic metal material, an oxidizing agent, and a material having a reducing action, and forming a high dielectric constant gate insulating film on the silicon substrate by generating a chemical reaction in the reaction chamber.
According to the second aspect of the present invention, in the method for manufacturing the semiconductor device according to the first aspect, the oxidizing gas and the material gas having a reducing action are first introduced into the reaction chamber, and, shortly thereafter, the organic metal material is introduced into the reaction chamber.
According to the third aspect of the present invention, the method for manufacturing a semiconductor device provided with a high dielectric constant gate insulating film made of a metal oxide formed on the semiconductor substrate comprises the steps of: forming a plurality of active regions in an element separating region for forming an MIS-type semiconductor device in each active region; forming a high dielectric constant insulating film on a semiconductor substrate using a CVD method by a chemical reaction of an organic metal material containing a metal for forming a metal oxide, an oxidizing agent, and a material having a reducing action; patterning, after forming a conductive layer on the high dielectric constant insulating film, the high dielectric constant insulating film and the conductive layer for forming the gate insulating film made of the high dielectric constant insulating film and a gate electrode made of the conductive layer, and forming the MIS-type transistors by forming a source and drain regions by ion implantation of a desired conductivity type impurity into the active regions using each gate electrode as a mask.
According to the fourth aspect of the present invention, in the method for manufacturing a semiconductor device according to the first aspect, the thickness of the high dielectric constant insulating film is determined by the magnitude of the dielectric constant of the high dielectric constant insulating film.
According to the fifth aspect of the present invention, in the method for manufacturing a semiconductor device according to the fourth aspect, a thicker high dielectric constant insulating film is formed when the high dielectric constant insulating film has a higher dielectric constant.
According to the sixth aspect of the present invention, in the method for manufacturing a semiconductor device according to the first aspect, THF (tetrahydrofuran) is used as the material having a reducing action.
According to the seventh aspect of the present invention, in the method for manufacturing a semiconductor device according to the first aspect, wherein the metal oxide is selected from the group of metal oxides consisting of ZrO2 (zirconium oxide), HfO2 (hafnium oxide), Al2O3 (aluminum oxide), BST ((Ba, Sr)TiO2), Ta2O5 (tantalum oxide), and TiO2 (titanium oxide).
According to the eighth aspect of the present invention, in the method for manufacturing a semiconductor device according to the first aspect, the semiconductor substrate is made of silicon.
According to the ninth aspect of the present invention, a semiconductor device, in which a plurality of active regions are formed in an element separating region formed in a semiconductor substrate, and each active region has a high dielectric constant gate insulating film made of a metal oxide, comprises: the high dielectric constant gate insulating film which is constituted by a high dielectric constant insulating film formed by a chemical reaction of an organic metal material including a metal for forming a metal oxide, an oxidizing agent, and a material having a reducing action.
According to the tenth aspect of the present invention, in a semiconductor device according to the ninth aspect, the metal oxide is selected from the group of metal oxides consisting of ZrO2 (zirconium oxide), HfO2 (hafnium oxide), Al2O3 (aluminum oxide), BST ((Ba, Sr)TiO2), Ta2O5 (tantalum oxide), and TiO2 (titanium oxide).
According to the eleventh aspect of the present invention, in a semiconductor device according to the ninth aspect, the semiconductor substrate is made of silicon.